Various information recording techniques have been developed following the increase in volume of information processing in recent years, Particularly, the areal recording density of a HDD using the magnetic recording technique has been increasing at an annual rate of about 100%. Recently, the information recording capacity exceeding 200 GB has been required per 2.5-inch magnetic recording medium adapted for use in a HDD or the like. In order to satisfy such a requirement, it is necessary to realize an information recording density exceeding 400 Gbits/inch2.
In order to achieve the high recording density in a magnetic recording medium for use in a HDD or the like, the perpendicular magnetic recording system has been proposed in recent years. In a perpendicular magnetic recording medium for use in the perpendicular magnetic recording system, the easy magnetization axis of a magnetic recording layer is adjusted so as to be oriented in a direction perpendicular to the surface of a substrate. As compared with the conventional in-plane magnetic recording system, the perpendicular magnetic recording system can suppress a so-called thermal fluctuation phenomenon in which the thermal stability of a recorded signal is degraded due to superparamagnetism so that the recorded signal is lost, and thus is suitable for increasing the recording density.
As the perpendicular magnetic recording medium for use in the perpendicular magnetic recording system, a CoCrPt—SiO2 perpendicular magnetic recording medium (see T. Oikawa et. al., IEEE Trans. Magn, vol. 38, 1976-1978 (2002)) is proposed because it exhibits high thermal stability and excellent recording characteristics. In this CoCrPt—SiO2 perpendicular magnetic recording medium, a magnetic recording layer has a granular structure in which nonmagnetic grain boundaries where SiO2 is segregated are formed between magnetic grains in the form of continuously grown columnar Co crystals with a hop (hexagonal closest packed) structure, thereby achieving both miniaturization of the magnetic grains and an improvement in coercive force Hc. It is known that an oxide is used for forming nonmagnetic grain boundaries (nonmagnetic portions between magnetic grains), and it is proposed to use, for example, one of SiO2, Cr2O3, TiO, TiO2, and Ta2O5 (JP-A-2006-024346).